Atom chip having two conductive strips for an ultra-cold atom inertial sensor, and associated sensor

Abstract

An atom chip (Ach) for an ultra-cold atom sensor, the atom chip includes a first pair of waveguides, a second pair of waveguides, the projections of the guides along X and the guides along Y′ in the plane XY forming, at their intersection, a first parallelogram with a centre O and having a first surface, a first conductive strip and a second conductive strip arranged such that their respective projection in the plane XY forms, at their intersection, a second parallelogram also with a centre O and having a second surface, the strips being designed to be flowed through by DC currents, an intersection between the first and the second surface being greater than or equal to 40% of the first surface.

The invention claimed is: 
     
       1. An atom chip (Ach) for an ultra-cold atom sensor, comprising a measurement plane XY defined by an axis X and an axis Y that are orthogonal, said measurement plane being normal to an axis Z, the atom chip comprising:
 a first pair of waveguides consisting of a first and a second waveguide (CPWX 1 , CPWX 2 ) that are coplanar, parallel to one another and arranged symmetrically on either side of an axis whose projection in the plane XY is along the axis X, called guides along X, 
 a second pair of waveguides consisting of a first and a second waveguide (CPWY′ 1 , CPWY′ 2 ) that are coplanar, parallel to one another and arranged symmetrically on either side of an axis whose projection in the plane XY is along an axis Y′ different from the axis X, called guides along Y′, 
 the guides along X being electrically insulated from the guides along Y′; 
 the projections of the guides along X and the guides along Y′ in the plane XY forming, at their intersection, a first parallelogram (P 1 ) with a centre O and having a first surface (S 1 ), 
 a first conductive strip (W 1 ) and a second conductive strip (W 2 ) arranged such that their respective projection in the plane XY forms, at their intersection, a second parallelogram (P 2 ) also with a centre O and having a second surface (S 2 ), said strips being designed to be flowed through by DC currents, 
 an intersection between the first (S 1 ) and the second (S 2 ) surface being greater than or equal to 40% of the first surface (S 1 ). 
 
     
     
       2. The atom chip according to  claim 1 , wherein the first and the second strip are respectively oriented along a first (D 1 ) and a second (D 2 ) diagonal of said first parallelogram. 
     
     
       3. The atom chip according to  claim 1 , wherein the first (W 1 ) and the second (W 2 ) strip are perpendicular to one another. 
     
     
       4. The atom chip according to  claim 1 , wherein said second pair of waveguides is perpendicular to said first pair of waveguides, the axis Y′ then being coincident with the axis Y. 
     
     
       5. The atom chip according to  claim 1 , wherein said strips are perpendicular to one another and said pairs of waveguides are perpendicular to one another and oriented at 45° from said strips. 
     
     
       6. The atom chip (Ach) for an ultra-cold atom sensor according to  claim 1 , comprising:
 at least one additional pair of guides along X that are further away from the axis X than the first pair, and 
 at least one additional pair of guides along Y′ that are further away from the axis Y′ than the second pair. 
 
     
     
       7. An ultra-cold atom sensor allowing a rotational velocity (Ω z ) measurement along at least the axis Z comprising:
 an atom chip (ACh) according to  claim 1  placed in a vacuum chamber, 
 an atom source (S) designed to generate a cloud of ultra-cold atoms close to said plane XY of said atom chip, 
 said ultra-cold atoms having, in the phase of initializing the implementation of the sensor, a superposition of internal states |a> and |b> 
 a generator (GB) for generating a homogeneous magnetic field (B 0 ), 
 at least one processor (UT), at least one DC current or voltage generator (GDC) connected to said strips and at least one microwave current or voltage generator (GMW) connected to said waveguides, 
 said waveguides and said strips being configured, in the phase of implementing the sensor, so as to:
 modify the energy of said ultra-cold atoms so as to create a potential minimum for the ultra-cold atoms in the internal state |a> and a potential minimum for the ultra-cold atoms in the internal state |b>, thus forming a first (T 1 ) and second (T 2 ) ultra-cold atom trap, a trap making it possible to immobilize a cloud of ultra-cold atoms in an internal state different from the other trap, at a controlled distance from said measurement plane, and 
 spatially separate the two traps and move said traps (T 1 , T 2 ) along at least one first closed path (TZ) contained within a plane perpendicular to Z, and travelled in one direction by the ultra-cold atoms of the first trap and in the opposite direction by the ultra-cold atoms of the second trap, 
 
 the sensor furthermore comprising an optical intensity detection system (SDET) designed to measure at least one population of said ultra-cold atoms in one said internal state. 
 
     
     
       8. The ultra-cold atom sensor according to  claim 7 , wherein, in the sequence of separating and moving said traps:
 the guides along X of the first pair are passed through simultaneously by microwave signals with angular frequencies ωa or ωb, at certain times called first set of times, 
 at least one of the guides along Y′ of the second pair is passed through by a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa′ and a microwave signal with an angular frequency ωb′, at certain times called second set of times having times in common with the first set of times, 
 the strips each being flowed through by a constant current during the separation, the movement and the recombination of said traps, 
 where applicable the guides along X of said at least one additional pair are also successively passed through simultaneously by microwave signals with angular frequencies ωa or ωb, at certain times different from the first set of times. 
 
     
     
       9. The ultra-cold atom sensor according to  claim 7 , wherein, in the sequence of separating and moving said traps:
 the guides along Y′ of the second pair are passed through simultaneously by microwave signals with angular frequencies ωa′ or ωb′, at certain times called first set of times, 
 at least one of the guides along X of the first pair is passed through by a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa and a microwave signal with an angular frequency ωb, at certain times called second set of times having times in common with the first set of times, 
 the first and second strips each being flowed through by a constant current during the separation, the movement and the recombination of said traps, 
 where applicable the guides along Y′ of the at least one additional pair are also passed through simultaneously by microwave signals with angular frequencies ωa′ or ωb′, at certain times different from the first set of times. 
 
     
     
       10. The ultra-cold atom sensor according to  claim 7 , furthermore allowing a rotational velocity measurement along the axes X and Y′,
 wherein said waveguides and said strips are furthermore configured so as
 to move said traps (T 1 , T 2 ) along a second closed path (TX) contained within a plane perpendicular to X, during the rotational velocity (Ωx) measurement along the axis X, 
 to move said traps (T 1 , T 2 ) along a third closed path (TY′) contained within a plane perpendicular to Y′, during the rotational velocity (Ωy′) measurement along the axis Y′, 
 said closed paths being travelled in one direction by the ultra-cold atoms of the first trap and in the opposite direction by the ultra-cold atoms of the second trap, the second and third paths each comprising at least one first portion located at a first height (h 1 ) from the plane XY and a second portion located at a second height (h 2 ) strictly greater than the first height. 
 
 
     
     
       11. A sensor according to  claim 10 , wherein, when implementing the measurement of the rotational velocity (Ωx) along the axis X by generating the second closed path (TX),
 the guides along X of the first pair are passed through simultaneously by microwave signals with angular frequencies ωa or ωb, at certain times called third set of times, 
 the guides along Y′ of the second pair are simultaneously passed through by a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa′ and a microwave signal with an angular frequency ωb′ in order to switch from the first height to the second height, at certain times called fourth set of times having times in common with the third set of times,
 the first and second strips are each flowed through by a constant current during the separation, the movement and the recombination of said traps, 
 where applicable the guides along X of said at least one additional pair are also passed through simultaneously by microwave signals with angular frequencies ωa or ωb, at certain times different from the third set of times. 
 
 
     
     
       12. The sensor according to  claim 10 , wherein, when implementing the measurement of the rotational velocity (Ωy′) along the axis Y′ by generating the third closed path (TY′),
 the guides along Y′ of the second pair are passed through simultaneously by microwave signals with angular frequencies ωa′ or ωb′, at certain times called third set of times, 
 the waveguides along X of the first pair are simultaneously passed through by a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa and a microwave signal with an angular frequency ωb in order to switch from the first height to the second height, at certain times called fourth set of times having times in common with the third set of times,
 the first and second strips are each flowed through by a constant current during the separation, the movement and the recombination of said traps, 
 where applicable the guides along Y′ of said at least one additional pair are also passed through simultaneously by microwave signals with angular frequencies ωa′ or ωb′, at certain times different from the third set of times. 
 
 
     
     
       13. A matrix atom chip (AchM) according to  claim 1 , comprising:
 a first set of N first conductive strips (W 1   n ) indexed n and a second set of M second conductive strips (W 2   m ) indexed m that are perpendicular to one another and respectively form N rows and M columns of a matrix, the strips of the first set being electrically insulated from the strips of the second set, 
 axes Xk indexed k are defined along first diagonals (Dk) of the matrix and axes YI indexed I are defined along second diagonals (D′I) perpendicular to the first diagonals, 
 the matrix chip also comprising first pairs of waveguides along each axis Xk and second pairs of waveguides along each axis YI, each pixel of the matrix forming an elementary chip (Ach(n,m)). 
 
     
     
       14. The matrix atom chip according to  claim 13 , furthermore comprising:
 for each axis Xk, at least one additional pair of guides along Xk that is further away from the axis Xk than the first pair, 
 for each axis YI, at least one additional pair of guides along YI that is further away from the axis YI than the second pair. 
 
     
     
       15. An ultra-cold atom sensor comprising:
 a matrix atom chip according to  claim 13 , 
 an atom source (S) designed to generate a cloud of ultra-cold atoms close to said plane XY of said atom chip, 
 a generator (GB) for generating a homogeneous magnetic field (B 0 ), 
 at least one processor (UT), at least one DC current or voltage generator (GDC) designed to control electric currents in said strips, and at least one microwave current or voltage generator (GMW) connected to said waveguides, 
 an optical intensity detection system (SDET), 
 the sensor being designed to measure, according to requirements and in a reconfigurable manner, at least one acceleration (ax, ay) and/or rotational velocity (Ωx, Ωy, Ωz) in a direction corresponding to that of the axis Xk and/or the axis YI, and/or a rotational velocity (Ωz) along the axis Z, from said elementary chips. 
 
     
     
       16. A method for measuring a rotational velocity about at least one axis called measurement axis, using an ultra-cold atom sensor comprising an atom chip, said atom chip being placed in a vacuum chamber and comprising a measurement plane XY defined by an axis Z and an axis Y that are orthogonal, said measurement plane being normal to an axis Z, the atom chip comprising:
 a first pair of waveguides consisting of a first and a second waveguide (CPWX 1 , CPWX 2 ) that are coplanar, parallel to one another and arranged symmetrically on either side of an axis whose projection in the plane XY is along the axis X, called guides along X, 
 a second pair of waveguides consisting of a first and a second waveguide (CPWY′ 1 , CPWY′ 2 ) that are coplanar, parallel to one another and arranged symmetrically on either side of an axis whose projection in the plane XY is along an axis Y′, called guides along Y′, 
 the guides along X being electrically insulated from the guides along Y′; the projections of the guides along X and the guides along Y′ in the plane XY forming, at their intersection, a first parallelogram (P 1 ) with a centre O and having a first surface (S 1 ), 
 a first conductive strip (W 1 ) and a second conductive strip (W 2 ) arranged such that their respective projection in the plane XY forms, at their intersection, a second parallelogram (P 2 ) also with a centre O and having a second surface (S 2 ), said strips being designed to be flowed through by DC currents, 
 an intersection between the first and the second surface being greater than or equal to 40% of the first surface (S 1 ), 
 the method comprising, for measuring the rotational velocity along Z, the steps of: 
 A: generating a cloud of said ultra-cold atoms, including phases of dispersing said atoms, of cooling said atoms, of initializing said atoms in at least one internal state |a> and of trapping a cloud of said ultra-cold atoms in a local potential minimum, said trapping being achieved through the flow of DC currents through the first and the second strip; 
 B: initializing internal states by coherently superposing said ultra-cold atoms between said state |a> and an internal state |b> different from |a> through a first pulse π/2; 
 C: spatially separating a cloud of said atoms with said internal state |a> in a trap (T 1 ) from a cloud of said atoms with said internal state |b> in another trap (T 2 ), and moving said traps in opposing directions along a closed path contained within a plane perpendicular to the measurement axis and initialized from the point O: by applying a predetermined microwave-frequency current or voltage to said waveguides in a predetermined sequence, and by applying a constant DC current or voltage value to the first and second strips; 
 D: recombining said internal states |a> and |b> by applying a second pulse π/2 to said ultra-cold atoms and then measuring the number of atoms in an internal state chosen from among at least |a> and |b>; 
 E: determining the Sagnac phase of said ultra-cold atoms and calculating the rotational velocity of said sensor along said measurement axis. 
 
     
     
       17. The measurement method according to  claim 16 , in order to measure a rotational velocity about the axis Z, wherein, during step C, said sequence includes applying, at certain times, a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa and a microwave signal with an angular frequency ωb to one of the guides along X of the first pair, or applying a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa′ and a microwave signal with an angular frequency ωb′ to one of the guides along Y′ of the second pair. 
     
     
       18. The measurement method according to  claim 16 , in order to measure a rotational velocity about the axis X or the axis Y′, wherein, during step C, said sequence includes:
 in order to measure the rotational velocity about the axis X, applying, at certain times, a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa and a microwave signal with an angular frequency ωb, simultaneously to the two guides along X of the first pair, 
 in order to measure the rotational velocity about the axis Y′, applying, at certain times, a microwave signal formed by the superposition of a microwave signal at an angular frequency ωa′ and a microwave signal with an angular frequency ωb′, simultaneously to the two guides along Y′ of the second pair.